SPI on Bullseye

General Discussion
1

I’m brand new to using SPI and trying to connect an LCD (Digital Visions DOGM128-6 Graphic) to a BeagleBone Black and do a basic “Hi BBB” message on the display with C. I’m starting to use Bullseye. I have wired up the display as follows:

BB → Display
P9_15 (GPIO) → A0/Pin38
P9_21 (spi) → SI / Pin 36
P9_22(spi_sclk) → CLK/SCL /pin 37

I am writing in C.

Here’s the output of beagle-version

root@BeagleBone:/home/debian/projects/APSDev# beagle-version
eeprom:[A335BNLT00C02411SBB02285]
model:[TI_AM335x_BeagleBone_Black]
dogtag:[BeagleBoard.org Debian Bullseye IoT Image 2023-09-02]
bootloader:[microSD-(push-button)]:[/dev/mmcblk0]:[U-Boot SPL 2022.04-ge0d31da5 (Aug 04 2023 - 18:48:26 +0000)]:[location: dd MBR]
bootloader:[eMMC-(default)]:[/dev/mmcblk1]:[U-Boot SPL 2019.04-00002-gc9b3922522 (Aug 24 2020 - 16:42:18 -0500)]:[location: dd MBR]
bootloader:[eMMC-(default)]:[/dev/mmcblk1]:[U-Boot 2019.04-00002-gc9b3922522]:[location: dd MBR]
UBOOT: Booted Device-Tree:[am335x-boneblack-uboot-univ.dts]
UBOOT: Loaded Overlay:[BB-ADC-00A0.kernel]
UBOOT: Loaded Overlay:[BB-BONE-eMMC1-01-00A0.kernel]
UBOOT: Loaded Overlay:[BB-I2C2-RTC-DS3231]
UBOOT: Loaded Overlay:[BB-SPIDEV1-00A0]
kernel:[5.10.168-ti-r82]
nodejs:[v12.22.12]
/boot/uEnv.txt Settings:
uboot_overlay_options:[enable_uboot_overlays=1]
uboot_overlay_options:[uboot_overlay_addr4=/lib/firmware/BB-W1_P9.12-00A0.dtbo]
uboot_overlay_options:[uboot_overlay_addr5=/lib/firmware/BB-I2C2-RTC-DS3231.dtbo]
uboot_overlay_options:[uboot_overlay_addr6=/lib/firmware/BB-SPIDEV1-00A0.dtbo]
uboot_overlay_options:[disable_uboot_overlay_video=1]
uboot_overlay_options:[disable_uboot_overlay_audio=1]
uboot_overlay_options:[enable_uboot_cape_universal=1]
pkg check: to individually upgrade run: [sudo apt install --only-upgrade <pkg>]
pkg:[bb-cape-overlays]:[4.14.20210821.0-0~bullseye+20210821]
pkg:[bb-customizations]:[1.20240119.0-0~bullseye+20240119]
pkg:[bb-usb-gadgets]:[1.20240717.0-0~bullseye+20240717]
pkg:[bb-wl18xx-firmware]:[1.20230703.0-0~bullseye+20240703]
pkg:[kmod]:[28-1]
WARNING:pkg:[librobotcontrol]:[NOT_INSTALLED]
pkg:[firmware-ti-connectivity]:[20210315-3]
groups:[debian : debian adm kmem dialout cdrom floppy audio dip video plugdev users systemd-journal input render bluetooth netdev i2c gpio admin tisdk weston-launch cloud9ide]
cmdline:[console=ttyS0,115200n8 bone_capemgr.uboot_capemgr_enabled=1 root=/dev/mmcblk0p1 ro rootfstype=ext4 rootwait coherent_pool=1M net.ifnames=0 lpj=1990656 rng_core.default_quality=100 quiet]
dmesg | grep remote
[   12.972301] remoteproc remoteproc0: wkup_m3 is available
[   43.861187] remoteproc remoteproc0: powering up wkup_m3
[   43.861229] remoteproc remoteproc0: Booting fw image am335x-pm-firmware.elf, size 217148
[   43.861537] remoteproc remoteproc0: remote processor wkup_m3 is now up
[   59.897907] remoteproc remoteproc1: 4a334000.pru is available
[   59.922567] remoteproc remoteproc2: 4a338000.pru is available
dmesg | grep pru
[   59.897907] remoteproc remoteproc1: 4a334000.pru is available
[   59.922567] remoteproc remoteproc2: 4a338000.pru is available
dmesg | grep pinctrl-single
[   12.356102] pinctrl-single 44e10800.pinmux: 142 pins, size 568
dmesg | grep gpio-of-helper
[   12.357927] gpio-of-helper ocp:cape-universal: Failed to get gpio property of 'P8_03'
[   12.357958] gpio-of-helper ocp:cape-universal: Failed to create gpio entry
[   13.286115] gpio-of-helper ocp:cape-universal: Allocated GPIO id=0 name='P8_03'
[   13.286418] gpio-of-helper ocp:cape-universal: Allocated GPIO id=1 name='P8_04'
[   13.286623] gpio-of-helper ocp:cape-universal: Allocated GPIO id=2 name='P8_05'
[   13.286828] gpio-of-helper ocp:cape-universal: Allocated GPIO id=3 name='P8_06'
[   13.287315] gpio-of-helper ocp:cape-universal: Allocated GPIO id=4 name='P8_07'
[   13.287547] gpio-of-helper ocp:cape-universal: Allocated GPIO id=5 name='P8_08'
[   13.287757] gpio-of-helper ocp:cape-universal: Allocated GPIO id=6 name='P8_09'
[   13.288100] gpio-of-helper ocp:cape-universal: Allocated GPIO id=7 name='P8_10'
[   13.288321] gpio-of-helper ocp:cape-universal: Allocated GPIO id=8 name='P8_11'
[   13.288536] gpio-of-helper ocp:cape-universal: Allocated GPIO id=9 name='P8_12'
[   13.288848] gpio-of-helper ocp:cape-universal: Allocated GPIO id=10 name='P8_13'
[   13.289059] gpio-of-helper ocp:cape-universal: Allocated GPIO id=11 name='P8_14'
[   13.289252] gpio-of-helper ocp:cape-universal: Allocated GPIO id=12 name='P8_15'
[   13.289460] gpio-of-helper ocp:cape-universal: Allocated GPIO id=13 name='P8_16'
[   13.289661] gpio-of-helper ocp:cape-universal: Allocated GPIO id=14 name='P8_17'
[   13.289864] gpio-of-helper ocp:cape-universal: Allocated GPIO id=15 name='P8_18'
[   13.290067] gpio-of-helper ocp:cape-universal: Allocated GPIO id=16 name='P8_19'
[   13.290255] gpio-of-helper ocp:cape-universal: Allocated GPIO id=17 name='P8_20'
[   13.290459] gpio-of-helper ocp:cape-universal: Allocated GPIO id=18 name='P8_21'
[   13.290667] gpio-of-helper ocp:cape-universal: Allocated GPIO id=19 name='P8_22'
[   13.290869] gpio-of-helper ocp:cape-universal: Allocated GPIO id=20 name='P8_23'
[   13.291066] gpio-of-helper ocp:cape-universal: Allocated GPIO id=21 name='P8_24'
[   13.291252] gpio-of-helper ocp:cape-universal: Allocated GPIO id=22 name='P8_25'
[   13.291482] gpio-of-helper ocp:cape-universal: Allocated GPIO id=23 name='P8_26'
[   13.291688] gpio-of-helper ocp:cape-universal: Allocated GPIO id=24 name='P8_27'
[   13.292015] gpio-of-helper ocp:cape-universal: Allocated GPIO id=25 name='P8_28'
[   13.292246] gpio-of-helper ocp:cape-universal: Allocated GPIO id=26 name='P8_29'
[   13.292439] gpio-of-helper ocp:cape-universal: Allocated GPIO id=27 name='P8_30'
[   13.292644] gpio-of-helper ocp:cape-universal: Allocated GPIO id=28 name='P8_31'
[   13.292860] gpio-of-helper ocp:cape-universal: Allocated GPIO id=29 name='P8_32'
[   13.293058] gpio-of-helper ocp:cape-universal: Allocated GPIO id=30 name='P8_33'
[   13.293271] gpio-of-helper ocp:cape-universal: Allocated GPIO id=31 name='P8_34'
[   13.293459] gpio-of-helper ocp:cape-universal: Allocated GPIO id=32 name='P8_35'
[   13.293664] gpio-of-helper ocp:cape-universal: Allocated GPIO id=33 name='P8_36'
[   13.293863] gpio-of-helper ocp:cape-universal: Allocated GPIO id=34 name='P8_37'
[   13.294064] gpio-of-helper ocp:cape-universal: Allocated GPIO id=35 name='P8_38'
[   13.294267] gpio-of-helper ocp:cape-universal: Allocated GPIO id=36 name='P8_39'
[   13.294468] gpio-of-helper ocp:cape-universal: Allocated GPIO id=37 name='P8_40'
[   13.294684] gpio-of-helper ocp:cape-universal: Allocated GPIO id=38 name='P8_41'
[   13.294898] gpio-of-helper ocp:cape-universal: Allocated GPIO id=39 name='P8_42'
[   13.295093] gpio-of-helper ocp:cape-universal: Allocated GPIO id=40 name='P8_43'
[   13.295315] gpio-of-helper ocp:cape-universal: Allocated GPIO id=41 name='P8_44'
[   13.295520] gpio-of-helper ocp:cape-universal: Allocated GPIO id=42 name='P8_45'
[   13.295712] gpio-of-helper ocp:cape-universal: Allocated GPIO id=43 name='P8_46'
[   13.296017] gpio-of-helper ocp:cape-universal: Allocated GPIO id=44 name='P9_11'
[   13.296232] gpio-of-helper ocp:cape-universal: Allocated GPIO id=45 name='P9_12'
[   13.296444] gpio-of-helper ocp:cape-universal: Allocated GPIO id=46 name='P9_13'
[   13.296685] gpio-of-helper ocp:cape-universal: Allocated GPIO id=47 name='P9_14'
[   13.296884] gpio-of-helper ocp:cape-universal: Allocated GPIO id=48 name='P9_15'
[   13.297088] gpio-of-helper ocp:cape-universal: Allocated GPIO id=49 name='P9_16'
[   13.297277] gpio-of-helper ocp:cape-universal: Allocated GPIO id=50 name='P9_17'
[   13.297483] gpio-of-helper ocp:cape-universal: Allocated GPIO id=51 name='P9_18'
[   13.297692] gpio-of-helper ocp:cape-universal: Allocated GPIO id=52 name='P9_19'
[   13.297886] gpio-of-helper ocp:cape-universal: Allocated GPIO id=53 name='P9_20'
[   13.298091] gpio-of-helper ocp:cape-universal: Allocated GPIO id=54 name='P9_21'
[   13.298311] gpio-of-helper ocp:cape-universal: Allocated GPIO id=55 name='P9_22'
[   13.298551] gpio-of-helper ocp:cape-universal: Allocated GPIO id=56 name='P9_23'
[   13.298763] gpio-of-helper ocp:cape-universal: Allocated GPIO id=57 name='P9_24'
[   13.299267] gpio-of-helper ocp:cape-universal: Allocated GPIO id=58 name='P9_25'
[   13.299509] gpio-of-helper ocp:cape-universal: Allocated GPIO id=59 name='P9_26'
[   13.299727] gpio-of-helper ocp:cape-universal: Allocated GPIO id=60 name='P9_27'
[   13.300045] gpio-of-helper ocp:cape-universal: Allocated GPIO id=61 name='P9_28'
[   13.300284] gpio-of-helper ocp:cape-universal: Allocated GPIO id=62 name='P9_29'
[   13.300490] gpio-of-helper ocp:cape-universal: Allocated GPIO id=63 name='P9_30'
[   13.300701] gpio-of-helper ocp:cape-universal: Allocated GPIO id=64 name='P9_31'
[   13.300928] gpio-of-helper ocp:cape-universal: Allocated GPIO id=65 name='P9_41'
[   13.301127] gpio-of-helper ocp:cape-universal: Allocated GPIO id=66 name='P9_91'
[   13.301335] gpio-of-helper ocp:cape-universal: Allocated GPIO id=67 name='P9_42'
[   13.301525] gpio-of-helper ocp:cape-universal: Allocated GPIO id=68 name='P9_92'
[   13.301537] gpio-of-helper ocp:cape-universal: ready
dmesg | grep wlcore
lsusb
Bus 001 Device 002: ID 0846:9030 NetGear, Inc. WNA1100 Wireless-N 150 [Atheros AR9271]
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
END

Here is the output from config-pin

root@BeagleBone:/home/debian/projects/APSDev# config-pin -q P9_21

Current mode for P9_21 is:     spi

root@BeagleBone:/home/debian/projects/APSDev# config-pin -q P9_22

Current mode for P9_22 is:     spi_sclk

root@BeagleBone:/home/debian/projects/APSDev# config-pin -q P9_15

Current mode for P9_15 is:     gpio

I have connected a scope to each line one at a time (just one channel on the scope in use)
When I run my program, the AO line (P9_15) toggles as it should.
But I never see any activity from P9_21 or P9_22. And nothing shows on the display.

Here’s my code for the ARM side.

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/spi/spidev.h>
#include <gpiod.h>
#include <string.h>
#include <sys/types.h>

#define SPI_DEVICE "/dev/spidev1.0"
#define GPIO_CHIP "gpiochip1"
#define GPIO_A0 16 // P9-15 (GPIO1_16)
#define WIDTH 128
#define HEIGHT 64

static int spi_fd;
static struct gpiod_line *a0_line;

void spi_write(u_int8_t *data, size_t len, int is_data) {
    if (gpiod_line_set_value(a0_line, is_data) < 0) {
        perror("Failed to set A0");
        return;
    }
    struct spi_ioc_transfer tr = {
        .tx_buf = (unsigned long)data,
        .len = len,
        .speed_hz = 1000000,
        .bits_per_word = 8,
    };
    if (ioctl(spi_fd, SPI_IOC_MESSAGE(1), &tr) < 0) {
        perror("SPI write failed");
    }
}

void init_display() {
    u_int8_t init[] = {
        0xA2, // Bias 1/9
        0xA0, // ADC select
        0xC8, // COM reverse
        0xA6, // Display normal
        0xA4, // All points off
        0x40, // Start line 0
        0x2F, // Power control: all on
        0x27, // V0 regulator (1:5)
        0x81, 0x20, // Contrast
        0xAF, // Display on
    };
    spi_write(init, sizeof(init), 0);
    usleep(100000); // 100ms delay
}

void clear_display() {
    u_int8_t buf[WIDTH];
    memset(buf, 0, WIDTH);
    for (int page = 0; page < 8; page++) {
        u_int8_t cmd[] = {0xB0 + page, 0x10, 0x04};
        spi_write(cmd, 3, 0);
        spi_write(buf, WIDTH, 1);
    }
}

void draw_text(const char *text, int x, int page) {
    static const u_int8_t font[128][5] = {
        ['H'] = {0x1F, 0x04, 0x04, 0x1F, 0x00},
        ['I'] = {0x00, 0x1F, 0x00, 0x00, 0x00},
        [' '] = {0x00, 0x00, 0x00, 0x00, 0x00},
        ['B'] = {0x1F, 0x15, 0x15, 0x0A, 0x00},
    };
    u_int8_t cmd[] = {0xB0 + page, 0x10 + (x >> 4), 0x00 + (x & 0x0F)};
    spi_write(cmd, 3, 0);
    for (int i = 0; text[i]; i++) {
        spi_write((u_int8_t *)font[(unsigned char)text[i]], 5, 1);
    }
}

int main() {
    spi_fd = open(SPI_DEVICE, O_RDWR);
    if (spi_fd < 0) {
        perror("Failed to open SPI");
        return 1;
    }
    u_int8_t mode = SPI_MODE_0;
    u_int32_t spi_speed = 1000000;
    if (ioctl(spi_fd, SPI_IOC_WR_MODE, &mode) < 0) {
        perror("Failed to set SPI mode");
        close(spi_fd);
        return 1;
    }
    if (ioctl(spi_fd, SPI_IOC_WR_MAX_SPEED_HZ, &spi_speed) < 0) {
        perror("Failed to set SPI speed");
        close(spi_fd);
        return 1;
    }

    struct gpiod_chip *chip = gpiod_chip_open_by_name(GPIO_CHIP);
    if (!chip) {
        perror("Failed to open GPIO chip");
        close(spi_fd);
        return 1;
    }
    a0_line = gpiod_chip_get_line(chip, GPIO_A0);
    if (!a0_line) {
        perror("Failed to get A0 line");
        gpiod_chip_close(chip);
        close(spi_fd);
        return 1;
    }
    if (gpiod_line_request_output(a0_line, 0, 0) < 0) {
        perror("Failed to request A0 output");
        gpiod_line_release(a0_line);
        gpiod_chip_close(chip);
        close(spi_fd);
        return 1;
    }

    init_display();
    clear_display();
    draw_text("HI BBB", 10, 4);

    gpiod_line_release(a0_line);
    gpiod_chip_close(chip);
    close(spi_fd);
    return 0;
}

Not to confuse the issue, but ultimately, I want to use this with one of the PRUs.

1 Like
2

is there a spidev driver loaded? if so that will consume those pins
why not use CS0 vs gpio

3

shouldn’t this be spidev0.0 for P9_21/22
why not use CS0 vs a gpio pin?

4

Depends if it’s alias’d or not; ls -al /dev/spi* should be able to remove all doubt.

5

@amf99 @lranders

As I said I’m really new to SPI. This is my first project with it. This is the only device in the system that will use SPI, so I have Chip Select pin (#40) tied low per the data sheet. So it should always be selected. I’m using P9_15 into the chip’s A0 line L=Command, H=data on it’s pin 38. I also have the RESET line tied high for now. I’m such a newbie I don’t know how I would use CS (P9_17?) instead of the GPIO on P9_15.

Also, once I switched to spiddev0.0, compiled and ran the code, I now see the expected square wave on CLK. It swings from 0 to 3.3V. The data line has corresponding waveform but is only swinging 3.3v to 3V. Seems something is bad wrong with that!!!

6

for data, 3.0 is (should be) ok.

7

If I wanted to use different pins, in case P9_21 is bad, what are the corresponding devices (spidev#.#) for the different pin sets?

What should spidev#.# be if I use P9_29 & P9_31? And where is this documented?

8

If it was me, I would also make sure to use the correct CS line,
simply because if you get out-of-sync, for any reason whatsoever,
the Display won’t have any way of knowing when any given
packet of data is supposed to start.

Forgot about the C/D line when driving Displays for a second. Sounds right.

I am somewhat dubious about the data line though…
If the CLK is able to swing down to 0V, it stands to reason that MOSI should do the same.
Can it go to 0V if say, you disconnect it from the Display?

Speaking of VIL, a quick look at the DC Characteristics for a SSD1306 gives me 0.2xVDD;
in other words MOSI must be below 0.6V to register as a zero.

9

Consult either the Schematic or the datasheet for the AM335x.

10

spidev0.x, the x is CS0 or CS1
this should be spidev1.x

11

So theoretically, I can just change

#define SPI_DEVICE "/dev/spidev0.0"

to

#define SPI_DEVICE "/dev/spidev0.1"

and then connect data to P9_29 and clock to P9_31 just to rule out an issue with P9_21?

12

my bad, my above post should have been spidev1
no, spidev0.0 to spidev1.0
and rewire the pins

13

Done. On the scope, I get a nice square wave on P9_31. But P9_29 is high and when the clock pulses up, there is a slight ripple increase on P9_29.

The Data line (P9_29) is not plugged in to the display or breadboard and I have changed both the scope leads and the jumper wire plugged in to P9_29. The scope is getting ground from P9_2 I have even swapped the scope leads between CLK and DATA and get the same result. Ideas?

Here is the scope screenshot.

NewFile1
NewFile1800×480 71 KB

So it doesn’t look like the hardware is damaged but some sort of setup issue. I don’t know how we’d write code that would cause this line to just ripple a bit.

root@BeagleBone:/home/debian/projects/APSDev# config-pin -q P9_31

Current mode for P9_31 is:     spi_sclk

root@BeagleBone:/home/debian/projects/APSDev# config-pin -q P9_29

Current mode for P9_29 is:     spi

root@BeagleBone:/home/debian/projects/APSDev#

@lranders

root@BeagleBone:/home/debian/projects/APSDev# ls -al /dev/spi*
crw------- 1 root root 153, 0 Apr 14 22:02 /dev/spidev0.0
crw------- 1 root root 153, 1 Apr 14 22:02 /dev/spidev0.1
crw------- 1 root root 153, 2 Apr 14 22:02 /dev/spidev1.0
crw------- 1 root root 153, 3 Apr 14 22:02 /dev/spidev1.1

/dev/spi:
total 0
drwxr-xr-x  2 root root   80 Jan  1  2000 .
drwxr-xr-x 18 root root 3560 Apr 14 22:02 ..
lrwxrwxrwx  1 root root   12 Apr 14 22:02 0.0 -> ../spidev0.0
lrwxrwxrwx  1 root root   12 Apr 14 22:02 0.1 -> ../spidev0.1

and @lranders

with P9_29 disconnected from the display and just connected to the scope, I get the blue line in the screenshot ~3.1V. I don’t think I’ve seen that go low.

14

the slight increase in the blue when the sclk goes high is typical, i get the same. on my setup.
one other thing, depending on your wire lengths, ya might want to start with a low spi clock 1M or so

15

If you want to cut down on unknown variables, you can google spidev_test.

It’s one of the testing tools provided with the Linux kernel.

16

If you want a definitive test, just set the data pin back to gpio and use gpioset to wiggle it.

Then you know if it can do HI and LO as expected.